1. Field of the Invention
The invention is related to non-destructively testing the integrity of package seals and particularly to testing small semi-rigid, flexible, and multi-cavity blister packages for defects of all sizes using vacuum and vision testing.
2. Brief Description of the Related Art
Differential pressure vacuum leak detection is commonly used to detect leaks in hermetically sealed packages. However, to detect leaks in packaging using vacuum leak detection, ample air must be contained inside the package to reliably detect defective packages. Small semi-rigid, flexible, and multi-cavity blister packages do not have enough air inside the package to reliably detect defects by simple vacuum decay methods.
The Ratio of air in the package to air in the chamber must be as large as possible for sensitive and accurate leak testing. Flexible chamber walls allow for the chamber to adjust to a flexible package area, but are still unable to be reliable with certain packages. Due to the small amount of air present in a blister cavity, the flexible chamber may evacuate the air from the cavity, equalizing the pressure before any measurements can take place. Methods of testing multi-cavity blister packages and other small packages using flexible chambers and vacuum decay, although not destructive, do not reliably detect large leaks.
Water submersion testing is also used to test small packages, which is destructive to the product as well and does not provide accurate results. Water submersion detects defects by having an operator visually observe air bubbles produced from submerged packages, which is unreliable and does not detect small defects. Water submersion inspection of all packages during production is not possible in most cases due to the destructive nature of the test.
In both of these foregoing detection methods, there is no indication of which blister cavity is defective and the reliability of the test results cannot be guaranteed. The location of a leak or package defect is beneficial to the process and control of packaging.
Non-contact sensor applications are capable of detecting the location of defective blister cavities, but are not reliable and effective for several reasons. The high sensitivity of the displacement sensors and the critical positioning of product inside the cavities may produce false measurements. Laser deflection is very sensitive to print and reflectivity of the surface material of the blister pack and may not be a suitable solution for certain materials.
Non-contact sensor methods can be destructive depending on the vacuum levels used during testing. If the product has a leak, the activity of the flexible blister cavity material is unpredictable due to equalization of the pressure inside the cavity. The cavity material may remain domed after pressure has equalized producing false results. If the non-contact sensor application requires pulling higher levels of vacuum without supporting the flexible package area with a flexible chamber wall, a package material may experience plastic deformation, in which it maintains a stretched position. These arguments apply to all testing processes that use non-contact sensory technology combined with controlled pressure environments such as disclosed in U.S. Pat. Nos. 6,687,622 B2; 5,082,366; 5,363,968; 6,167,751; 5,880,359; 5,763,765; 4,907,443; 6,763,702; and 4,850,696; United States Published Applications 2004/0057043A1 and 2004/0057043A1; and JP 406258175A.
In view of the foregoing, prior technology and methods of testing packaging for leaks are destructive, contingent on the properties of the package material, not sensitive enough for small packages and unreliable under certain circumstances.